1. Field of the Invention
The present invention relates to a positioning device for a magnetic disk memory constructed as a rotational positioner comprising a pedestal forming a part of a magnet system and carrying a positioner shaft whereby positioning arms which carry magnetic heads and clamp bracket arms for the magnet system are provided on the positioner shaft.
2. Description of the Prior Art
Technical development in magnetic disk memories continues to constantly work towards higher storage capacities, both with respect to the track density and the bit density as characteristics for the storage capacity per disk surface, on the one hand, and in view of the mechanical structure in order to accommodate as many magnetic disks as possible in a prescribed mounting space, on the other hand. An example of this is the so-called 51/4" fixed disk memory for which a mounting space having a mounting height of 82.5 mm and a base area of 146 mm.times.243 mm as a unit size has crystallized as a standard by analogy to the dimensions of competing floppy disk drives.
In addition to the attempt to accommodate as many magnetic disks as possible in this prescribed mounting space, i.e. to continue the development of the mechanical structure of the magnetic disk pack and its disposition in the housing of the magnetic disk memory, however, there are also attempts to improve the magnetic head positioner device in order to improve access time, precise positioning and, therefore, sensing reliability. A significant step in the direction towards higher storage densities in the magnetic disk memories was achieved by way of a positioning method in which the magnetic heads are no longer positioned absolutely relative to the data tracks of the magnetic disks. Instead, the position of the positioner is determined with respect to servo tracks with the assistance of track position information which is permanently stored on a servo disk. Given this positioning technique, the positioner device is a defining and integral part of the servo control loop. Accordingly, the mechanical properties of the positioner device are decisive factors for access time, access precision and the stability of the servo control loop.
Basically, two different types of positioner devices are known, the linear positioner and the rotational positioner. Given linear positioners, a positioner carriage to which the magnetic head positioning arms are secured is moved in the radial direction relative to the magnetic disk pack during the track selection, being moved, for example, by way of a moving coil system. The rotational positioner has a pivoting part which is constructed of a number of positioner arms which carry the magnetic heads. The pivoting part is pivotally seated on a positioner shaft disposed parallel to the axis of the disk pack and comprises a pair of brackets at the side facing away from the pivot arms. The brackets carry either a coil which is deflected relative to stationary magnets, or carry a magnet, whereby the excited coil is then stationarily disposed. In the former case, the rotational positioner is therefore designed as a swinging coil positioner; it is designed as a magnetic armature positioner in the latter case. Both types of rotational positioners are equivalent per se, at least in comparison to the linear positioner. The rotational positioner is very frequently employed given today's standard, smaller magnetic disk memories; its mass actually to be moved is slighter, it can be constructed smaller and therefore uses less energy. Overall, it is therefore faster and easier to control.
Known rotational positioners for multi disk memories are constructed such that pivot arms each having a pair of magnetic heads resiliently disposed directly thereon are provided, the pair of magnetic heads being allocated to mutually-facing disk surfaces of neighboring magnetic disks. Pivot arms are clamped to a hub with the interposition of shims and the hub is, in turn, seated on the positioner shaft. Given known rotational positioners, this shaft is, in turn, fixed to the housing of the magnetic disk memory, usually at one side, but sometimes at both sides.
There is, however, a disadvantage given this structure of the rotational positioner disclosed for example, in the publication IEEE Transactions on Magnetics, Vol. Mag-17, No. 4, July 1981, pp. 1392 et seq., in the publication Electronics, Apr. 21, 1982, pp. 181 et seq, or in the publications Mini-Microsystems, February 1983, pp. 143 et seq. The pivot part is composed of a plurality of parts that must be aligned relative to one another. Depending on the embodiment, either the entire appertaining pivot arm with the magnetic head mount must be replaced for changing magnetic heads, i.e. the pivot part must be dismantled, or even the rotational positioner must be removed as a unit, since the magnetic head mount is only accessible from the direction of the disk pack and can only be released from the pivot arm from this direction. In any case, repairs therefore require complicated dismantling and subsequent readjustments in order to realign the magnetic head systems or, respectively, the pivot arms to one another with the correct height and position.